Portable power tools such as line trimmers are normally powered by electric motors or small, typically single cylinder internal combustion engines. In either case, some mechanism is usually provided by which the operating speed of the motor or engine, and thus the operating speed of the workpiece driven by the motor or engine, can be increased and decreased by an operator of the power tool. Often, this mechanism takes the form of a trigger that may be depressed or squeezed by the operator. For example, U.S. Pat. No. 3,844,360 to Green et al. shows a chain saw powered by a two cycle engine and having two independently operable triggers. When either of the triggers is squeezed, it operates a throttle lever on the engine.
Portable power tools having internal combustion engines are also often provided with some means for ceasing operation of the engine when the operator no longer desires to work with the unit. One popular method of accomplishing this is through the use of an on/off or kill switch which grounds the supply of electricity to the spark plug. The '360 patent to Green et al., for instance, discloses the use of a separate on/off switch in the ignition circuit. Similarly, U.S. Pat. No. 4,286,675 to Tuggle shows a narrow profile power handle for a line trimmer and the like having an ignition kill switch situated near a hand grip portion of a rear handle.
For power tools such as line trimmers in which the engine is normally carried behind the operator, however, an ignition kill switch disposed on or near the engine would require the operator to remove one or both hands from their normal operating positions in order to manipulate the switch. However, if the manual actuators for the engine throttle and the kill switch are mounted proximate the operator's hands, then some provision must be made for retaining both the actuators themselves and their linkages with the engine in a cover or housing situated between them and the engine. When this cover is removed for servicing, loose components of the assembly are easily lost.